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100%, the main challenge will be privacy and e2e encryption. There is prior art we can draw on.

Similar if we want something akin to FB groups with private membership, events, and content

Private posts/feeds/groups is one of the biggest things missing from ATProto at this point.

Once they solve that it will really take off beyond just a better Twitter.

Another effort that could help is the lexicon-community. The goal is to create a number of lexicon that can be reused across apps.

Calendar, locations, and events is one of the first they are considering